1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to a scroll compressor which can smooth an operation of an orbiting scroll and prevent overturn thereof by forming a thrust bearing surface at an upper surface of a rotation preventing member for preventing rotation of the orbiting scroll.
2. Description of the Related Art
Generally, a compressor which is one of the main components of a refrigerating cycle apparatus compresses refrigerant gas at low temperature and low pressure introduced from an evaporator and discharges it at a high temperature and high pressure.
The compressor can be divided into a reciprocating type, a scroll type, a centrifugal type, and a vane type.
The scroll compressor sucks, compresses, and discharges gas by using an orbiting movement of an orbiting scroll having a wrap of involute shape.
FIG. 1 is a longitudinal section view showing a scroll compressor in accordance with the conventional art; and FIG. 2 is a disassembled perspective view showing a compression unit of the scroll compressor in accordance with the conventional art.
As shown, in the conventional scroll compressor, an upper frame 2 is fixed to an inner upper portion of a hermetic case 1, and a lower frame 3 is fixed to an inner lower portion of the case 1.
A stator 4 and a rotor 5 constituting a motor are installed between the upper frame 2 and the lower frame 3.
A crank shaft 6 which is rotated together as the rotor 5 rotates is engaged to a center of the rotor 5.
A fixed scroll 7 having a wrap of involute shape 7a is installed at the upper frame 2 with a predetermined interval, and an orbiting scroll 8 having a wrap of involute shape is installed below the fixed scroll 7.
A key groove 8b for inserting a key 9b of an oldham coupling 9 which will be explained later is formed at lower both sides of the orbiting scroll 8.
The crank shaft 6 is engaged to a lower portion of the orbiting scroll 8, thereby orbiting the orbiting scroll 8.
An oldham coupling 9 for preventing rotation of the orbiting scroll 8 is slidably engaged between the orbiting scroll 8 and the upper frame 2.
The oldham coupling 9 is composed of a body 9a of a ring shape and upper and lower keys 9b and 9c formed at upper and lower portions of the body 9a. 
An insertion hole 2a for inserting the crank shaft 6 is formed at a center of the upper frame 2, and a step portion 2b having a height h1 is formed at an upper surface of the upper frame 2 around the insertion hole 2a. 
A key groove 2c for inserting the key 9c of the oldham coupling 9 is formed at one side of the upper surface of the upper frame 2, and an oil groove 2d for supplying oil to a thrust bearing surface B formed at the upper surface of the upper frame 2 is formed at another side thereof.
As shown in FIG. 2, a height h2 of the body 9a of the oldham coupling 9 is formed to be lower than that h1 of the step portion 2b formed at the upper surface of the upper frame 2.
This indicates that the step portion 2b where the thrust bearing surface B is formed can support the orbiting scroll 8 but the body 9a of the oldham coupling 9 can not support the orbiting scroll 8.
Also, oil is contained at the lower portion of the case 1 to be supplied to a sliding part (a contact part between the orbiting scroll and the thrust bearing surface). A suction pipe 10 for sucking refrigerant gas is formed at a lateral lower portion of the case 1, and a discharge pipe 11 for discharging the refrigerant gas is formed at the upper portion thereof. An unexplained reference numeral 7b denotes a discharge port.
In the conventional scroll compressor, when the rotor 5 is rotated by applied current, the crank shaft 6 is rotated and thereby the orbiting scroll 8 is orbited by having an eccentric distance of the crank shaft 6 as a radius.
At this time, the orbiting scroll 8 is prevented from being rotated by the oldham coupling 9 and orbits.
As the orbiting scroll 8 makes the orbit movement, a compression chamber P is formed between the fixed scroll 7 and the orbiting scroll 8, and the compression chamber P is gradually decreased, compresses the sucked refrigerant gas, and discharges it to the discharge pipe 11 through the discharge port 7b. 
In the process that the orbiting scroll 8 makes the orbit movement by being engaged to the fixed scroll 7 to suck, compress, and discharge the refrigerant, force is applied to the orbiting scroll 8 towards a shaft direction, a radius direction, and a tangent direction by gas compression pressure or dead load of the orbiting scroll.
Herein, force towards the shaft direction influences on the orbiting movement of the orbiting scroll the most. According to this, the force towards the shaft direction has to be well supported to make the orbiting scroll orbit smoothly.
To this end, in the conventional art, the thrust bearing surface B is formed at the upper surface of the step portion 2b of the upper frame 2 which supports the lower surface of the orbiting scroll, and oil is supplied to the thrust bearing surface B.
In order to supply oil to the thrust bearing surface B, an oil passage hole 2e is formed in the upper frame 2 by being connected to the oil groove 2d formed at the upper surface of the step portion 2b of the upper frame 2, and the oil passage hole 2e is connected to the insertion hole 2a. 
According to this, oil is pumped by an oil pump (not shown) engaged to a lower end of the crank shaft 6 as the crank shaft 6 rotates, and the pumped oil is sucked along an oil passage 6a of the crank shaft 6. The sucked oil is supplied to the oil groove 2d through the insertion hole 2a and the oil passage hole 2e, and introduced into the thrust bearing surface B, thereby performing a lubrication operation.
As aforementioned, in order to support the shaft direction load of the orbiting scroll 8 smoothly and induce the smooth orbiting movement of the orbiting scroll 8, the thrust bearing surface B has to always support the lower portion of the orbiting scroll 8.
However, in the conventional scroll compressor, since the thrust bearing surface B is fixed to the upper surface of the step portion 2b of the upper frame 2, the orbiting scroll makes the orbiting movement by exceeding a range of the thrust bearing surface B when a pressure of the refrigerant gas is drastically increased or an orbiting scroll having a high wrap is adopted.
When the orbiting scroll 8 makes the orbit movement by exceeding the range of the thrust bearing surface B, the thrust bearing surface B does not support the shaft direction load properly. According to this, the orbiting scroll 8 does not perform the orbit movement smoothly and can be overturn,
Therefore, an object of the present invention is to provide a scroll compressor which can smoothen an operation of an orbiting scroll and prevent overturn thereof by forming a thrust bearing surface at an upper surface of a rotation preventing member for preventing rotation of the orbiting scroll.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a scroll compressor comprising: an upper frame fixed in a case; a fixed scroll fixed to the upper frame and having a wrap of involute shape; an orbiting scroll installed between the frame and the fixed scroll and having a wrap of involute shape in order to form a compression chamber which consecutively moves by being engaged to the wrap of the fixed scroll; and a rotation preventing member slidably installed between the upper frame and the orbiting scroll towards a radius direction for preventing a rotation of the orbiting scroll and having a thrust bearing surface at an upper surface thereof which supports a shaft direction load of the orbiting scroll.
The rotation preventing member is composed of a ring type body having the thrust bearing surface and upper and lower keys formed at upper and lower portions of the body, in which the thrust bearing surface of the body supports a lower surface of the orbiting scroll.
A height of the body of the rotation preventing member is formed to be higher than that of a step portion formed at an upper surface of the frame.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.